1. Field of the Invention
This invention relates to prostheses which are inflatable after implantation by means of resealable valves, and particularly to configurations of such valves.
2. Description of the Prior Art
During plastic and reconstructive surgery, it is often necessary to implant an inflatable prosthesis as a means of expanding the tissue and skin in a localized area of the body. This can be done either with a short term or "long-dwelling tissue expander device". Both types of devices require that progressive injections of volume-expanding fluid be made by the physician through a self-sealing valve during successive postoperative outpatient procedures. This is preferably done by percutaneous injection of a silicone gel, saline or other fluid through the valve into a reservoir to fill the lumen of the prosthesis; however, it is often difficult to locate the injection valve among the surrounding tissue. Various means have been employed to determine the location of such valves, including manual palpation, as well as external magnetic devices which sense the position of magnetic material within the valve.
An example of a magnetic locator which is used to find the injection reservoir in a mammary prosthesis is shown in U.S. Pat. No. 4,467,125; however, the device is principally concerned with providing a reinforcing member surrounding the juncture of the valve and outer envelope, intended to prevent the envelope from folding over upon itself during implantation. A similar product is currently sold under the name "MAGNA-SITE", by McGhan Medical Corp. of Santa Barbara, Calif. The magnetic locator device sold with this product resembles a simple stud finder like those used in the carpentry trade, e.g., that shown in U.S. Pat. No. 3,845,384.
U.S. Pat. No. 4,222,374 discloses an external locating device having a magnetic sensor which determines the position of an implanted metallic cardiac infusion pump by direct juxtaposition of the sensor with the ferro-magnetic element. However, there is no reference of such a device being used to locate an inflatable prosthesis, particularly a mammary implant.
Another concern with inflatable prostheses is the formation of a tissue capsule surrounding the implant, which has been known to contract around and, in some patients, significantly compress the implant, causing a great deal of discomfort. Thickness of the tissue which forms the capsule has been found to be an important factor in the incidence of problems related to capsule contracture, which is a complication requiring the physician to either surgically or manually rupture the capsule.
One approach that has been suggested to avoid this problem is the use of an implant having an outer envelope which comprises a microtextured surface. The aim of providing such a service is to disrupt the capsular architecture and cause ingrowth of the tissue into the microtextured surface, which results in a thinner tissue capsule and lessens the risk of problems due to capsule contracture.
One such device, shown in U.S. Pat. No. 4,955,909, provides a textured surface on the implant from a tetrafluoroethylene (Teflon) that is fabricated in a net-like, three-dimensional grid structure.
Another approach is discussed in the article "Ion-Beam Microtexturing of Biomaterials", Medical Device and Diagnostic Industry, volume 6, number 4, Apr. 1984 which describes the use of ion-beam milling of a soft tissue prosthesis to produce microprojections on the surface of the outer envelope and the use of such implants to reduce capsule contracture.
Still another approach is suggested in U.S. Pat. No. 4,955,907, particularly the use of expanded polytetrafluoroethylene filaments which are attached to a stretch fabric backing in a loose weave configuration. Alternatively, silicone molded in geometric patterns may be employed to present the textured surface.
Another approach is discussed in U.S. Pat. No. 4,960,425, wherein a surgical prosthesis having a textured exterior surface formed of non-absorbent material free of pores and interstices is shown. The implant disclosed in this patent is made by molding a silicone envelope over a textured or porous mandrel with either hot or cold compression platens, which are said to create minute indentations, deformations and/or raised portions on the surface of the envelope having a width from 0.0003 to 0.10 inches and a depth from 0.0003 to 0.030 inches, such that the general appearance of the prosthesis is that of an opaque surface, slightly roughened at the touch.
Another approach, and one which is particularly preferred, is taken by U.S. Pat. No. 4,965,430, assigned to the instant assignee. This method prepares a three-dimensional mandrel by laser-drilling an array of blind holes in the surface of the mandrel, used for preparing a mould for a silicone envelope having an arrray of micropillars corresponding to the pattern of blind holes.
Still another device having a micro-textured surface is shown in U.S. Pat. No. 5,002,572, which discloses a mass transfer device having a fluid diffusing or transmitting surface in contact with the soft tissue, the tissue contacting surface being textured to provide a regular pattern of micropillars at least 100 microns in height with dimensions and interpillar spacing each no greater than 5000 microns.
A different approach to the above methods of avoiding capsule contracture is shown in U.S. Pat. No. 4,531,244, specifically, a mammary prosthesis having a plurality of firm protuberances covering the outer surface of the envelope is said to result in flow spaces so that, when the scar capsule contracts and compresses the protuberances, the mammary prosthesis has a spacer for displacement and remains soft. The patent further states that the protuberances, which have a specified height of between 1000-10,000 microns and a diameter between 1000-10,000 microns. This macrotextured surface is further said to provide greater localized pressure in pounds per square inch against the scar capsule in order to maintain a space for implant displacement.
In addition to the attention given above to valve location and tissue capsule contracture concerns, there have been numerous attempts to provide volume-adjustable, anatomically-shaped mammary implants, including tissue-expander devices. Accordingly, various valve and fill-tube designs have been proposed.
One approach has been to situate an injection valve and reservoir at a location remote from the prosthetic implant, the valve being coupled with a fill-tube feeding into a volume-adjustable lumen. Such arrangements are shown in U.S. Pat. Nos. 4,773,908; 4,643,733; and 4,944,749, and further embodied in various products sold by the Mentor Corporation, Goleta, Calif., as the "Becker Expander/Mammary Prosthesis". Once the prosthesis has been filled to the desired level, the remote valve, along with the fill-tube which links the valve to a fill port in the envelope, is uncoupled from the filling port and, once surgically removed, is not intended to be reconnected.
Another volume-adjustable prosthesis having self-contained injection valves is shown in U.S. Pat. No. 4,433,440. A pair of valves are joined with the outer envelope at a common area, unlike than the remotely located Becker valve. One of the valves leads directly into an inner lumen which is joined to the outer envelope, while the other valve leads directly into the outer lumen which surrounds the inner lumen. A difficulty in this type of device is that differential protrusion/expansion of the prosthesis cannot occur other than at the area where both of the valves are commonly joined with the outer envelope, versus areas remote from the valve site.
Accordingly there is still a need for a volume-adjustable prosthesis, particularly a mammary implant which is capable of assuming a variety of anatomical shapes. Further, there is a need for providing an integral valve to allow such a volume-adjustable implant to be filled to a desired level by a physician without post-operative surgical intervention, particularly by means of an external valve-location means that accurately determines the position of the valve. Still further, there is a need to provide a volume-adjustable prosthesis, particularly a mammary implant, which resists problems due to capsule contracture.